Method and apparatus for metal coating tubing



July 6, 1954 R. 1. HAHN METHOD AND APPARATUS FOR METAL COATING TUBING Filed Oct. '51, 1950 4 Sheets-Sheet l #1: Arron/vars July 6, 1954 R. HAHN 2,633,099

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1/1: Arr-05 vs Patented July 6, 1954 METHOD AND APPARATUS FOR METAL COATING TUBING Rea I. Hahn, Rochester, N. Y., assignor to General Motors Corporation, Detroit, Mich., a corporation of Delaware Application October 31, 1950, Serial No. 193,266

This invention relates to the coating of metal articles with a metal of lower melting point than the article to be coated, and more particularly to a method of and apparatus for coating either single-ply welded tubing or two-ply brazed tubing with a metal of lower melting point than the metal of the tubing.

An object of the invention is to facilitate the use of brazing or coating metal in a manner which avoids wasting it. To accomplish this object, disclosed embodiments of the invention comprise a crucible into which the brazing or coating metal is introduced, preferably as a wire, and an electrical coil surrounding the wire which is connected with an alternating current source of relatively high frequency, for example, at 400 volts and 980 cycles, when the coating metal is copper, such coil being capable of transmitting electrical energy sufficient to melt the coating or brazin metal in the crucible and to cause said metal to be projected in the crucible, above the article to be coated, as amound of molten metal through which such article is passed horizontally to receive metal for brazing or coating purposes. There is an enclosed chamber above the metal in the crucible into which reducing gas under pressure is introduced through ducts provided by wiper blocks through which the article to be coated passes in order to remove excess molten metal from said article and return the excess to the crucible and to provide an atmosphere in which oxidation of the article and the metal does not occur.

As described specifically herein the method and apparatus disclosed is employed to coat single-ply welded tubing or braze multi-ply tubing, but it should be apparent that the method and apparatus described can be used just as well to coat other articles, for example, a wire, a rod, or any other form of metal tubing.

Further objects and advantages of the present invention will be apparent from the following description, reference being had to the accompanying drawings, wherein preferred embodiments of the present invention are clearly shown.

In the drawings:

Figs. 1 and 2 constitute a plan view of a mill for making two-ply, copper brazed, steel tubing.

Fig. 3 is a plan view of brazing apparatus 20 shown diagrammatically 'in Fig. 2.

Fig. 4 is a sectional view on line 4 -4 of Fig. 3.

Figs. 5 and 6 constitute a diagram of a mill for making coated, welded steel tubing.

Fig. '7 is a longitudinal sectional view of the 18 Claims. (Cl. 117-114) 2 coating apparatus I30 of the mill as shown in Fig. 4.

Two steel strips S which move toward the left in Fig. 1 pass between pairs of scarfing rolls l and II which bevel the edges of the strip. The strips then pass through a lubricating device !2 and between pairs of rolls [3 of a former M which progressively shape the strips into a tube T in the manner shown in the patent to Nichols and Bish #2,195,751 dated April 2, 1949.

The tubing passes through a swedger l which compacts the plies of the tubing. Then the tubing passes left in Fig. 2 between pairs of electrode rolls H and [8 of a preheater l6 connected with a current source for the purpose of heating the tubing before it passes to the apparatus 20 for applying molten copper thereto to braze the plies of the tubing. After brazing the tubing passes through a cooler 60 having a jacket 6| through which water circulates. Then the tubing is wound on a reel 62 driven by a power mechanism 63 for the purpose of pulling the tubing through the brazing apparatus 20 and the cooler I0.

Referring to Figs. 3 and 4, the brazing apparatus 20 comprises a non-conducting base 2| supported above the floor by a frame 22 and supporting brackets 23 and 24 which support a refractory plate 25 having grooves 26 and providing a central opening 21 giving access to a refractory crucible 28 enclosed by a heat insulating body 29 supported by the plate 2| and surrounded by a non-conducting tube 30 surrounded by a shorter-conducting tube 3|. Tube 3| supports a coil 32 of flattened copper tubing having round ends 33 and 34 connected respectively by wires 35 and 36 with an alternating current sourcejfor example, at 400 volts and 960 cycles when the brazing metal is copper. Heat is conducted away from the coil 32 by the circulation of water through the coils. For this purpose the coil ends 33 and 34 are connected with non-conducting hoses 31 and 38. Coil ends 33 and 34 are supported by a non-conducting block 24a which screws 24b secure to bracket 24.

The opening 21 in plate 25 is closed by a refractory cover 40 having a hole 4| closed by a glass block 42 and having a hole 43 through which a copper wire is moved downwardly. The grooves 26 of plate 25 support metal blocks 45 providing aligned holes 46 through which the tubing T passes from right to left. Each block 45 provides an inclined duct 41 connected by pipe 48 and a hose 49 with a source of reducing gas under pressure. Blocks 45 are retained with- 3 in grooves 26 by clips which screws 5i attach to the blocks and which are attached to brackets and 24 by screws 52. A non-conducting jacket 53 supported by a plate 2i surrounds the coil and the sleeve 3i.

The high frequency A. C. current flowing through the coil 32 effects the melting of the copper wire as it is fed downwardly into the crucible and causes the metal in the crucible to be prolected upwardly as indicated by the dot-dash line 54 to form a mound of molten metal through which the tubing T passes while in an atmosphere of reducing gas flowing from the ducts ll. The metal readily wets the surface of the tubing and flows along it and the exces is wiped off and returned to the crucible 28 by the jets of compressed. reducing gas issuing from the ducts 4?. The amount of electrical energy used by the apparatus for melting the copper and for causing upward projection thereof is preferably about kva. of which about is used to melt the copper, the excess of the heat generated being absorbed by the tubing which i maintained, while within the apparatus 22 at a temperature above the melting point of copper. Since the tubing is preheated by the apparatus It, its rate of movement through the apparatus 263 can be increased because the preheating supplies a substantial portion of the heat units required. to elevate the temperature of the tubing above the melting point of the metal in the crucible 28.

A modified form of the apparatus 22 can be used in the coating of welded steel tubing produced by a mill shown in Figs. 5 and 6. A strip of metal S moving left in Fig. 5 is progressively formed by pairs of rolls IIIl, III, H2 and II3 into a tubing T having a butt seam which is welded as it is urged against spaced electrode rolls I It by a backup roll I I5 supported by a lever I I6 pivoted at H? on a bracket H8 and urged upwardly by constant pressure applied by compressed air within a bellows Iii-I mounted on a base I22. A pipe represented by a line I2I extends down between the edges of the strip so that it enters the tubing between the rolls I I I and I I 2 and then extends horizontally. Through this pipe a reducing atmosphere is introduced into the tubing.

The welding apparatus back-up roll construction constitutes no part of the present invention and may be such as shown in Nichols Patent No. 2,293,846, dated August 25, 1942, and in Hahn et al. Patent No. 2,492,572, dated December 27, 1949.

The bead formed on the tubing during the welding operation is removed by a tool I22. The tubing then passes between pairs of sizing rolls I23 and I24 and then between pairs of electrode rolls I26, HI and I28 of an annealer I having roll housings I2ta, IZ'Ia, IZSa and connecting tubes I29, all enclosing a reducing atmosphere.

- The tubing which has been heated by the annealer passes directly to an apparatus indicated at I! for coating it with a non-corrosive metal such as copper which fills up minute pores in the tubing and provides it with a coating which is rustproof. The tubing next passes through a cooling pipe I'Ifl which is surrounded by a jacket I'II through which cold water circulates. The tubing is then wound upon a reel I72 which is power driven to take up the slack in the tubing.

Referring to Fig. 7, the apparatus I30 comprises a non-conducting base plate I3! supported above the floor by frame members I32. Base I3I supports metal brackets I33 and I34 which support a non-conducting plate I35 having grooves I36 and having a central opening I3? providing access to a refractory crucible I33 surrounded by heat insulating material I32 supported by plate I3I and confined within a non-conducting sleeve Mil extending within a non-conducting sleeve I4I which supports a coil I42 of flattened copper tubing having round ends I43 and I44 connected respectively, with insulated wires I45 and I46 with a high frequency alternating current source preferably at 400 volts and 956 cycles. Heat is conducted from the coil M2 by circulating water through it. For this purpose non-conducting hoses I4! and I48 are clamped about the coil ends I43 and I44. These ends are supported by a non-conducting block I34a secured to bracket I34 by screws I341).

Plate I35 supports a refractory cylinder I53 having a refractory cover I5I supporting a glass plate I52 and having a hole I53 through which a wire W of copper, or other suitable metal, is in troduced. A portion of the coil I42 surrounds the tube I59 and is surrounded by a refractory cupshaped jacket I54 supported by the plate I35.

The grooves I36 of plate I35 receive metal blocks I55 having aligned holes I56 through which the tubing T passes from right to left. The righthand block I55 supports the tubing as it moves horizontally, but the left-hand block Ilia does not support the tubing since all portions of its hole I55 clear the tubing. Each block I55 has an obliquely disposed duct I5? connected by a pipe I533 and a hose I59 with a source of pressurized reducing gas which flows out through the ducts I51 to wipe oif excess metal received by the tube and to return the excess metal to the crucible I38. Blocks I55 are retained in groove I36 by clips I60 which screws ISI attach to the blocks and which screws I62 attach to brackets I33 and I34. An insulating tube I63 supported by plate I3I surrounds sleeve MI and the lower portion of coil I42.

The passage of electric current, for example, 400 volts A. C. at 960 cycles when the coating metal is copper, through the coil I42 causes heating of the crucible I38 and the tube I50 to a high temperature so that the wire W melt as it is fed downwardly. The molten metal of the wire fills the crucible. The passage of high frequency cur rent through coil I42 causes the molten metal in the crucible to rise up as indicated by the curved dot-dash line I54 to form a mound of molten metal through which the tubing passes. As the tubing passes through this mound it receives a coating of the metal which readily wet the tubing since it is in a reducing atmosphere provided by the gas flowing from the ducts I51.

The electrical energy used by the apparatus for melting copper and for causing upward pro jection thereof is preferably about 20 kva, the minor proportion of which supplies the heat for melting the copper, the excess of the heat generated being absorbed by the tubing at a temperature which is maintained, while in the ap paratus I30, above the melting point oi the metal in the crucible I33. Since the tubing passes directly from the annealer I23 to the coating apparatus I30, its rate of movement through the apparatus I30 can be increased because the annealer I28 supplies a substantial part of the heat units required to maintain the temperature of the tubing, while in the apparatus Hit, above the melting point of the metal in the crucible I38.

When an electric heating means of the character described herein is employed to heat the copper or other metal employed to braze or coat steel tubing, there is less waste of the coating metal due to the carrying of such metal out of the heating chamber by the moving tubing for the following reason. The level of the coating liquid is raised, above the level of the tubing, by the effect of the high frequency current, only in the area around the vertical axis of the heating chamber, as indicated by the dot and dash lines in Figs. 4 and 7. The levelof the coating metal adjacent the wall of the heating chamber is not raised so that the opening through which the tube passes out of the chamber is always above the level of the molten coating metal. Therefore there is no tendency for the moving tubing to drag the coating metal from the main supply outwardly through the exit opening through which the tubing passes. The tubing tends only to carry out of the heating chamber such surplus coating metal as sticks to the tube when it passes through the mound of metal at the central part of said chamber. This is substantially all blown off of the tubing and back into the heating chamber by the gas blast through the pipe or nozzle 48 at the left of either Fig. 4 or Fig. 7.

Both the apparatus shown in Fig. 4 and that shown in Fig. 7 can be used for copper coating welded steel tubing as well as forcopper brazing or multi-ply steel tubing. The height of the column, or mound of metal projected above the tubing is a function of the amount of electrical energy which is transmitted by the heating coil. However, the amount of electrical energy which can be employed'is limited by the capacity of the moving tubing to remove excess heat as fast as excess heat is generated. If the excess heat is not removed as fast as it is generated, the coating or brazing metal would be overheated. Therefore, the coil cannot be used to transmit more than a certain amount of energy and this determines the height of the mound or column of coating metal which can be obtained.

It should be equally apparent that the device of either Fig. 4 or Fig. 7 can be used to coat other articles than the specific form of tubing referred to with copper or some other metal of lower melting point than the article to be coated. For example, the element designated therein could be a wire, or a rod, or some different form of tubing, and the apparatus disclosed would be just as effective to coat such an article as it is to coat the particular types of tubing previously referred to.

If it is desired to employ a higher mound or column of the molten coating metal during the coating operation, it is desirable to use the form of the device shown in Fig. 7 of the drawings. Since, in the apparatus shown in Fig. 7, half of the heating coil is above the level of the coating metal, the efficiency of the coil is less than in the form of the device shown in Fig. 4 and more electrical energy can be employed without overheating of the metal and a higher column or mound of such metal can be obtained than if the apparatus of Fig. 4 is used. It will be desirable to vary the height of the column of coating metal when different metals are used, such as copper, tin and lead alloys, aluminum or brasses, for example, due to diiferent characteristics and melting points.

While the embodiments of the present invention as herein disclosed, constitute preferred forms, it is to be understood that other forms might be adopted.

What is claimed is as follows:

1. The method of brazing multi-ply metal tubing or coating welded tubing with a metal of lower melting point than that of the tubing which includes the steps of moving the tubing through a chamber containing in the lower part thereof a quantity of the coating metal, while maintaining the tubing at a level above the normal level of the coating metal therein when in a non-molten condition, heating the lower part of said chamber in which the coating metal is con tained by subjecting the lower part of such chamber to the heating effect of a high frequency electric current to a degree suflicient to melt such metal and to cause the level of the molten metal in the chamber to rise above the level of the tubing as the latter is moved through the chamber, subjecting the tubing as it leaves the chamber to a blast of non-oxidizing gas directed against the tubing at a point relatively close to an opening through which the tubing moves out of said chamber and introducing the coating metal into the chamber in unmelted form as the tubing is moved through said chamber.

2. The method of brazing multi-ply metal tubing or coating welded tubing with a metal of lower melting point than that of the tubing which includes the steps of moving the tubing through a chamber containing in the lower part thereof a quantity of the coating metal, While maintaining the tubing at a level above the normal level of the coating metal therein when in a non-molten condition, heating said chamber both above and below the level at which the tubing passes through the chamber by subjecting both parts of such chamber to the heating eifect of a high frequency electric current to a degree suilicient to melt such metal and to cause the level of the molten metal in the chamber to rise above the level of the tubing as the latter is moved through the chamber, subjecting the tubing as it leaves the chamber to a blast of nonoxidizing gas directed against the tubing at a point relatively close to an opening through which the tubing moves out of said chamber and introducing the coating metal into the chamber in unmelted form as the tubing is moved through said chamber.

3. The method of brazing multi-ply metal tubing or coating welded tubing with a metal of lower melting point than that of the tubing which includes the steps of moving the tubing through a chamber containing a quantity of the coating metal while maintaining the tubing at a level above the normal level of said metal therein, heating the coating metal in said chamber by use of high frequency electric current to a degree suiiicient to melt said metal and to cause the level of the molten metal to rise above the level of the tubing as the latter is moved through the chamber so that the tubing passes through the molten metal during its movement and introducing the coating metal into the chamber in unmelteol form during the passage of the tubing through said chamber.

4. The method of brazing multi-ply metal tubing or coating welded tubing with a metal of lower melting point than that of the tubing which includes the steps of moving the tubing through a chamber containing a quantity of the coating metal while maintaining the tubing at a level above the normal level of said metal therein, heating the lower part of the chamber in which the coating metal is contained by use of a high frequency electric current to a degree sulficient to melt said metal and to cause the level of the molten metal to rise above the level of the tubing as the latter is moved through the chamber so that the tubing passes through the molten metal during its movement and introduoing the coating meta-l into the chamber in unmelted form during the passage of the tubing through said chamber.

5. The method of brazing multi-ply metal tubing or coating welded tubing with a metal of lower melting point than that of the tubing which includes the steps of moving the tubing through a chamber containing a quantity of the coating metal while maintaining the tubing at a level above the normal level of said metal therein, heating the chamber in which the coating metal is contained, both above and below the level at which the tubing passes through such chamber, by use of a high frequency electric current, to a degree sufficient to melt said metal and to cause the level of the molten metal to rise above the level of the tubing as the latter is moved through the chamber so that the tubing passes through the molten metal during its movement and introducing the coating metal into the chamber in unmelted form during the passage of the tubing through said chamber.

6. The method of brazing multi-ply metal tubing or coating welded tubing with a metal of lower melting point than that of the tubing which comprises the steps of moving the tubing through a chamber which contains a quantity of the coating metal while maintaining the tubing at a level above the normal level of the metal therein while said metal is in a non-molten condition subjecting said chamber to the heating effect of a high frequency electric current so as to heat said chamber to a degree sufiicient to melt the coating metal and to cause the level of the molten metal to rise above the level of the tubing as the latter is moved through the chamher, so that the tubing passes through the molten metal during its movement, subjecting the tubing as it leaves the chamber to a blast of nonoxidizing gas directed under pressure against the tubing, at a point relatively close to an opening through which the tubing passes out of the chamber, for the purpose of removing any surplus of the coating metal and introducing the coating metal into the chamber in unmelted form during the coating operation.

7. Apparatus for brazing multi-ply metal tubing and for coating welded tubing with a metal of lower melting point than said tubing comprising, in combination, a chamber in which the tubing and the coating metal are heated, the lower part of which is adapted to contain a sup ply of the coating metal, openings in the wall of said chamber through which the tube to be coated passes, said openings being located above the normal level of the unmelted coating metal in said vessel so that the tubing passes through said chamber at a point above that level, means for moving the tubing through the chamber during the coating operation, a heating coil surrounding said chamber and connected to a source of electric current oi high frequency, said coil being effective to heat said chamber to a degree sufficient to melt the coating metal and to cause the molten metal to rise in said heating chamber to a level above that of the tubing so that the tubing passes through the coating metal as it is moved through said chamber.

8. Apparatus for brazing multi-ply metal tubing and for coating welded tubing with a metal of lower melting point than said tubing comprising, in combination, a chamber in which the tubing and the coating metal are heated, the lower part of which is adapted to contain a supply of the coating metal, openings in the wall of said chamber through which the tube to be coated passes, said openings being located above the normally level of the unmelted coating metal in said vesse1 so that the tubing passes through said chamber at a point above that level, means for moving the tubing through the chamber during the coating operation, a heating coil surrounding said chamber and connected to a source of electric current of high frequency, said coil being effective to heat said chamber to a degree sufficient to melt the coating metal and to cause the molten metal to rise in said heating chamber to a level above that of the tubing so that the tubing passes through the coating metal as it is moved through said chamber, and means directing a blast of non-oxidizing gas under pressure against said tubing adjacent the opening through which said tubing passes out of the heating chamber to remove any surplus coating metal.

9. Apparatus for brazing multi-ply metal tubing and for coating welded tubing with a metal of lower melting point than said tubing comprising, in combination, a chamber in which the tubing and the coating metal are heated, the lower part of which is adapted to contain a supply of coating metal, openings in the wall of said chamber through which the tube to be coated passes, said openings being located above the normal level of the unmelted coating metal in said vessel so that the tubing passes through said chamber at a point above that level, means for moving the tubing through the chamber during the coating operation, a heating coil surrounding said chamber and connected to a source of electric current of high frequency, said coil being efiective to heat said chamber to a degree sufiicient to melt the coating metal and to cause the molten metal to rise in said heating chamber to a level above that of the tubing so that the tubing passes through the coating metal as it is moved through said chamber, means directing a blast of non-oxidizing gas under pressure against said tubing adjacent the opening through which said tubing passes out of the heating chamber to remove any surplus coating metal, and means for maintaining a suflicient quantity of coating metal within the heating chamber during the coating operation.

10. Apparatus for brazing multi-ply metal tubing and for coating welded tubing with a metal of lower melting point than said tubing comprising, in combination, a chamber in which the tubing and the coating metal are heated, the lower part of which is adapted to contain a supply of the coating metal, openings in the wall of said chamber through which the tube to be coated passes, said openings being located above the normal level of the unmelted coating metal in said vessel so that the tubing passes through said chamber at a point above that level, means for moving the tubing through the chamber during the coating operation, a heating coil surrounding said chamber and connected to a source of electric current of high frequency, said coil being effective to heat said chamber to a degree sufficient to melt the coating metal and to cause the molten metal to rise in said heating chamber to a level above that of the tubing so that the tubing passes through the coating metal as it is moved through said chamber, means directing a blast of non-oxidizing gas under pressure against said tubing adjacent the opening through which said tubing passes out of the heating chamber to remove any surplus coating metal and means for continuously introducing unmelted casting metal in the heating chamber as the tubing to be coated is drawn through said chamber. a

11. Apparatus for brazing multi-ply meta1 tub ing and for coating Welded tubing with a metal of lower melting point than said tubing comprising, in combination, a chamber in which the tub ing and the coating metal are heated, the lower part of which is adapted to contain a supply of the coating metal, openings in the wall of said chamber through which the tube to be coated passes, said openings being located above the normal level of the unmelted coating metal in said vessel so that the tubing passes through said chamber at a point above that level, means for moving the tubing through the chamber during the coating operation, a heating coil surrounding the lower part of the heating chamber in which the coating metal is contained and connected to a source of electric current of high frequency, said coil being effective to heat said chamher to a degree sufficient to melt the coating metal and to cause the molten metal to rise in said heating chamber to a level above that of the tubing so that the tubing passes through the coating metal as it is moved through said chamber.

12. Apparatus for brazing multi-ply metal tubing and for coating welded tubing with a metal of lower melting point than said tubing comprising, in combination, a chamber in which the tubing and the coating metal are heated, the lower part of which is adapted to contain a supply of the coating metal, openings in the wall of said chamber through which the tube to be coated passes, said openings being located above the normal level of the unmelted coating metal in said vessel so that the tubing passes through said chamber at a point above that level, means for moving the tubing through the chamber during the coating operation, a heating coil connected to a source of electric current of of high frequency and surrounding the heating chamber both above and below the level at which the tubing to be coated passes through such chamber, said coil being effective to heat said chamber to a degree sufficient to melt the coating metal and to cause the molten metal to rise in said heating chamber to a level above that of the tubing, so that the tubing passes through the coating metal as it is moved through said' chamber.

13. Apparatus for brazing multi-ply metal tubing and for coating welded tubing with a metal of lowermelting point than said tubing comprising, in combination, a chamber in which the tubing and the coating metal are heated, the lower part of which is adapted to contain a supply of the metal, openings in the wall of said chamher through which the tube to be coated passes, said openings being located above the normal level of the unmelted coating metal in said vessel so that the tubing passes through said chamber at a point above that level, means for moving the tubing through the chamber during the coating operation, a tubular metallic heating coil connected to a source of electric current of high frequency and surrounding the heating chamber, said coil being effective to heat said chamber to a degree sufficient to melt the coating metal and .10 to cause the molten metal to rise in said heating chamber to a level above that of the tubing so that the tubing passes through the coating metal as it is moved through said chamber and means for circulating a cooling medium through said coil.

14. Apparatus for brazing multi-ply metal tubing and for coating welded tubing with a metal of lower melting point than said tubing comprising, in combination, a chamber in which the tubing and the coating metal are heated, the lower part of which is adapted to contain a supply of the coating metal, openings in the wall of said chamber through which the tube to be coated passes, said openings being located above the normal level of the unmelted coating metal in said vessel so that the tubing passes through said chamber at a point above that level, means for moving the tubing through the chamber during the coating operation, a heating coil connected to a source of electric current of high frequency and surrounding said heating chamber,

said coil being effective to heat said chamber to a degree sufficient to melt the coating metal and to cause said molten metal to rise adjacent the vertical axis of said chamber to a level higher than that of the tubing, while the metal adjacent the wall of said chamber remains at a level lower than that of the tubing, whereby the tubing is prevented from passing through the molten coating metal at a point adjacent the opening through which the tubing is moved out of such chamber and the transport of surplus coating metal out of said chamber by the tubing is reduced.

15. Apparatus for brazing multi-ply metal tubing and for coating welded tubing with a metal of lower melting point than said tubing comprising, in combination, a chamber in which the tubing and the coating metal areheated, the lower part of .which is adapted to contain a supply of the coating metal, openings in the wall of said chamber through which the tube to be coated passes, said openings being located above the normal level of the unmelted coating metal in said vessel so that the tubing passes through said chamber at a point above that level, means for moving the tubing through the chamber during the coating operation, a heating coil connected to a source of electric current of high frequency and surrounding said heating chamber, said coil being efiective to heat said chamber to a degree sufiicient to melt the coating metal and to cause said molten metal to rise adjacent the vertical axis of said chamber to a level higher than that of the tubing, while the metal adjacent the wall of said chamber remains at a level lower than that of the tubing, whereby the tubing is prevented from passing through the molten coating metal at a point adjacent the opening through which the tubing is moved out of such chamber and the transport of surplus coating metal out of said chamber by the tubing is reduced, and means for directing a blast of non-oxidizing gas under pressure against the tubing adjacent said last mentioned opening and in a direction substantially opposite to the direction of movement of the tubing in order to minimize the escape of the coating metal through said opening as the tubing is moved therethrough.

16. Apparatus for brazing multi-ply metal tubing and for coating welded tubing with metal of lower melting point than said tubing comprising, in combination, a chamber in which the tubing and the coating metal are heated, the

lower part of which is adapted to contain a supply of the coating metal, openings in the wall of said chamber through which the tube to be coated passes, said openings being located above the normal level of the umnelted coating metal in said vessel so that the tubing passes through said chamber at a point above that level, means for moving the tubing through the chamber during the coating operation, a heating coil connected to a source of electric current of high frequency and surrounding said heating chamher, said coil being effective to heat said chamber to a degree sufficient to melt the coating metal and to cause said molten metal to rise adjacent the vertical axis of said chamber to a level higher than that of the tubing, while the metal. adjacent the wall of said chamber remains at a level lower than that of the tubing, whereby the tubing is prevented from passing through the molten coating metal at a point adjacent the opening through which the tubing is moved out of such chamber and the transport of surplus coating metal out of said chamber by the tubing is reduced and a nozzle for directing a blast of non-oxidizing gas against the tubing adjacent said last mentioned opening, said nozzle being arranged at an angle to the path of movement of the tubing and discharging said gas in a direction substantially opposite to the direction of movement of the tubing, in order to minimize the escape of coating metal through said opening as the tubing is moved therethrough.

17. Apparatus for brazing multi-ply metal tubing and for coating welded tubing with a metal of lower melting point than said tubing comfor moving the tubing through the chamber during the coating operation, a heating coil surrounding said heating chamber and connected to a source of electric current of substantially 960 cycles frequency, said coil being effective to heat said chamber to a degree sufficient to melt the coating metal and to cause the molten metal to rise in said heating chamber to a level above that of the tubing so that the tubing passes through the coating metal as it is moved through said chamber.

18. Apparatus for brazing multi-ply metal tubing and for coating welded tubing with a metal of lower melting point than said tubing comprising, in combination, a chamber in which the tubing and the coating metal are heated, the lower part of which is adapted to contain a supply of the coating metal, openings in the wall of said chamber through which the tube to be coated passes, said openings being located above the normal level of the unmelted coating metal in said vessel so that the tubing passes through said chamber at a point above that level, means for moving the tubing through the chamber during the coating operation, a heating coil surrounding said chamber and connected to a source of electric current of high frequency, said coil being effective to heat said chamber to a degree sufficient to melt the coating metal and to cause the molten metal to rise in said heating chamber to a level above that of the tubing so that the tubing passes through the coating metal as it is moved through said chamber, said heating chamber having an opening in the wall thereof adapted to receive a wire formed of the coating metal which is moved into the chamber during the coating operation so as to maintain a predetermined quantity of the coating metal in said chamber.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 1,323,883 Lutz Dec. 2, 1919 1,424,171 Lee Aug. 1, 1922 1,424,181 Pritchard Aug. 1., 1922 1,531,730 Bundy Mar. 31, 1925 1,584,728 Case May 13, 1925 1,643,330 Barord Sept. 27, 1927 1,766,417 Watkin June 24:, 1930 1,896,416 Quarnstrom '7, 1933 2,337,357 Stuewer Dec. 21, 1943 2,344,589 Bogner Mar. 21, 1944 

1. THE METHOD OF BRAZING MULTI-PLY METAL TUBING OR COATING WELDED TUBING WITH A METAL OF LOWER MELTING POINT THAN THAT OF THE TUBING WHICH INCLUDES THE STEPS OF MOVING THE TUBING THROUGH A CHAMBER CONTAINING THE LOWER PART THEREOF A QUANTITY OF THE COATING METAL, WHILE MAINTAINING THE TUBING AT A LEVEL ABOVE THE NORMAL LEVEL OF THE COATING METAL THEREIN WHEN IN A NON-MOLTEN CONDITION, HEATING THE LOWE PART OF SAID CHAMBER IN WHICH THE COATING METAL IS CONTAINED BY SUBJECTING THE LOWER PART OF SUCH CHAMBER TO THE HEATING EFFECT OF A HIGH FREQUENCY ELECTRIC CURRENT TO A DEGREE SUFFICIENT TO MELT SUCH METAL AND TO CAUSE THE LEVEL OF THE MOLTEN METAL IN THE CHAMBER TO RISE ABOVE THE LEVEL OF THE TUBING AS THE LATTER IS MOVED THROUGH THE CHAMBER, SUBJECTING THE TUBING AS IT LEAVES THE CHAMBER TO A BLAST OF NON-OXIDIZING GAS DIRECTED AGAINST THE TUBING AT A POINT RELATIVELY CLOSE TO AN OPENING THROUGH WHICH THE TUBING MOVES OUT OF SAID CHAMBER AND INTRODUCING THE COATING METAL INTO THE CHAMBER IN UNMELTED FOAM AS THE TUBING IS MOVED THROUGH SAID CHAMBER.
 7. APPARATUS FOR BRAZING MULTI-PLY METAL TUBING AND FOR COATING WELDED TUBING WITH A METAL OF LOWER MELTING POINT THAN SAID TUBING COMPRISING, IN COMBINATION, A CHAMBER IN WHICH THE TUBING AND THE COATING METAL ARE HEATED, THE LOWER PART OF WHICH IS ADAPTED TO CONTAIN A SUPPLY OF THE COATING METAL, OPENINGS IN THE WALL OF SAID CHAMBER THROUGH WHICH THE TUBE TO BE COATED PASSES, SAID OPENINGS BEING LOCATED ABOVE THE NORMAL LEVEL OF THE UNMELTED COATING METAL IN SAID VESSEL SO THAT THE TUBING PASSES THROUGH SAID CHAMBER AT A POINT ABOVE THAT LEVEL, MEANS FOR MOVING THE TUBING THROUGH THE CHAMBER DURING THE COATING OPERATION, A HEATING COIL SURROUNDING SAID CHAMBER AND CONNECTED TO A SOURCE OF ELECTRIC CURRENT OF HIGH FREQUENCY, SAID COIL BEING EFFECTIVE TO HEAT SAID CHAMBER TO A DEGREE SUFFICIENT TO MELT THE COATING METAL AND TO CAUSE THE MOLTEN METAL TO RISE IN SAID HEATING CHAMBER TO A LEVEL ABOVE THAT OF THE TUBING SO THAT THE TUBING PASSES THROUGH THE COATING METAL AS IT IS MOVED THROUGH SAID CHAMBER. 